Data communication in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. A local area network (LAN) is an example of a subnetwork that provides relatively short-distance communication among the interconnected stations. In contrast, a wide area network (WAN) facilitates long-distance communication over links provided by public or private telecommunications facilities. The entities are typically software programs executing on hardware computer platforms which, depending on their roles within the network, may serve as end stations or intermediate stations. Examples of intermediate stations include routers, bridges and switches that interconnect communication links and subnetworks, whereas an end station may be a computer located on one of the subnetworks. More generally, an end station connotes a source of or target for data that typically does not provide routing or other services to other computers on the network.
A packet-switched network refers to a type of network in which relatively small units of data (i.e., packets) are routed through the network based on destination address information contained within each packet. Breaking communication down into packets allows the same data path to be shared among many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching and the Internet is generally a connectionless network.
End stations typically communicate by exchanging discrete packets or frames of data according to predefined protocols. In this context, a protocol represents a set of rules defining how the stations interact with each other to transfer data. The traffic flowing into a network device—e.g., a router, switch, bridge, server, and the like—is generally made up of multiple abstraction layers (e.g., the Open Systems Interconnection (OSI) model). Each of these logical layers generally relates to communications functions of a similar nature. Generally, each layer is responsible for providing some service to the layer above it, and similarly each layer may use services of the layer below it. The International Standards Organization (“ISO”) defined seven layers as a standard for computer networks in creating the OSI model. The layers are defined as follows: (1) the physical layer, (2) the data link layer, (3) the network layer, (4) the transport layer, (5) the session layer, (6) the presentation layer, and (7) the application layer. Generally, the physical layer is responsible for transmitting unstructured bits of information across a link. The data link layer generally provides error-free transfer of data frames over the physical layer, allowing layers above it to assume virtually error-free transmission over the link. The network layer is responsible for ensuring that any pair of systems in the network can communicate with each other, while the transport layer establishes a reliable communications stream between a pair of systems. The session layer generally facilitates the establishment of sessions between processes running on different sessions, by providing functionality for session establishment, maintenance and termination, as well as session support functionality such as security, name recognition services, and so on. Additionally, the presentation layer is responsible for the delivery and formatting of application layer information, while the application layer is responsive with the transfer and manipulating application data (e.g., transferring files, mail services, and so on).
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.